There exists a critical link between lifestyle, weight, and overall health. Extensive evidence has shown that lifestyle and behaviors, such as diet and physical activity, have a significant impact on the cause, prevention and treatment of many obesity-related diseases, including diabetes, high blood pressure, heart disease, and cancer. In fact, recent clinical studies have demonstrated that a modest weight loss of 5-7% can prevent or delay the development of Type 2 diabetes in high-risk individuals (Knowler W C, Barrett-Connor E, Fowler S E, Hamman R F, Lachin J M, Walker E A, et al. Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin. N Engl J Med. 2002 Feb. 7; 346(6):393-403; http://www.diabetesaustralia.com.au/PageFiles/763/Primarypreventionguideline.pdf), while weight loss associated with routine physical activity, such as walking, has been linked to better cardiac health and longer lifespan. Physiologically, weight gain occurs when total calorie intake exceeds total energy expenditure (http://www.fitbit.com/http://www.carefusion.com/medical-products/respiratory/cardiopulmonary-diagnostics/metabolic-carts-cpet-nutrition/metabolic-carts/oxycon-mobile.aspx; http://www.bodymedia.com/, http://www.actigraphcorp.com/), but maintaining a healthy energy balance requires easy and accurate methods to track energy expenditure and calorie intake.
Energy expenditure: Total energy expenditure (TEE) comprises primarily resting energy expenditure (REE), or known as resting metabolic rate or simply, metabolism, and physical activity-related energy expenditures (PAE). For most people who spend only a few hours per week on exercises, REE is the most important portion of energy expenditure, counting for more than 80% of TEE. One of the most accurate and frequently used methods to measure REE is indirect calorimetry, which is the gold standard method recommended by the American College of Sports Medicine, American Dietetic Association and World Health Organization. Indirect calorimetry measures the oxygen consumption and carbon dioxide production rates while breathing. However, successful and traditional indirect calorimetry relies on bulky, expensive, and difficult-to-operate equipment, which limits its applications for individuals in real-world conditions (e.g., at home, work, or in the gym). The limited portable versions of existing indirect calorimetry devices are still expensive and the results can be highly operator-dependent, necessitating the guidance of a trained professional. Mault et al. disclosed several designs of portable devices (U.S. Pat. Nos. 6,468,222 B1; 4,917,108; 5,038,792; 5,178,155; 5,179,958; and 5,836,300) to measure REE based on indirect calorimetry. These patents feature generally specific flow designs for passing both inhalations and exhalations of the user, and inclusion of a scrubber to remove CO2 from breath to determine oxygen consumption. Orr et al. (U.S. Pat. No. 6,475,158 B1) disclosed a design of metabolic analyzer including a mixing chamber and calibration gas to measure oxygen consumption. In addition, Kofoed et al. disclosed a different flow design to measure flow rate and infrared detection chamber to measure CO2 production in breath (U.S. Pat. No. 5,789,660). Tao and Forzani (PCT 13/493,552) disclosed a portable metabolic analyzer based on a colorimetric sensing technology to track REE. However, in order to accurately determine REE, one must create innovative methods to quickly and correctly collect breath sample, accurately measure the flow rate of breath, monitor the temperature of breath, and mitigate water condensation issue in the portable device.
PAE tracking traditionally relies on self-reporting, which is tedious and inaccurate. More recently, physical sensors, such as accelerometers and GPS trackers, and heart rate monitors (Zhu, F. Q., M. Bosch, et al. (2010), John, D., S. Liu, et al. (2011)) have been used to track different activities. Each sensor can track certain types of physical activities, but none of them can monitor all types of physical activities. For example, the accelerometer-based sensors cannot detect physical activities, such as weight lifting and light office work-related activities while sitting on a desk, and GPS trackers do not work well for indoor activities due to limited satellite signals. There is a need to track physical activities that cannot be measured with the current physical sensors. From the type, intensity and time duration of each physical activity, the associated PAE is determined with various algorithms. For a given type, intensity and time duration of a physical activity (e.g. running), the energy expenditure varies with the gender, weight, age, skill, and shoes of the individual, and also with road and weather conditions. To improve the accuracy of the PAE, one must improve not only the physical sensors, but also the algorithms that can correctly translate the measured physical activity into energy expenditure.
Calorie intake tracking: The traditional approach to assess calorie intake and TEE is self-reporting, which has led to important discoveries relating lifestyle behaviors to disease development. However, studies, including those by R. P. Troiano and P. S. Freedson reported in American Journal of Preventive Medicine, vol. 38, pp. 682-683, June 2010, have also revealed the pitfalls of self-reporting—there is a clear need for more quantitative and objective methods. To meet this need, new devices, smartphone, and web applications that monitor calorie intake (Zhu, F. Q., M. Bosch, et al. (2010)) and TEE (Kozey, S. L., K. Lyden, et al. (2010), Matthews, C., K. Chen, et al. (2008)) have been developed. Examples include the recording of food consumption from digital photos and videos based on image recognition algorithms. These methods are useful but still subject to errors and usability issues. Speech recognition may also be used to track calorie intake (U.S. Pat. No. 007392193B2). However, recording every item in the total calorie intake is tedious, and also subject to errors due to the person's limited ability to correctly estimate the portion of each consumed item, and accurately memorize and record every meal.
Tracking energy expenditure and calorie intake in an integrated device: To guide individuals to maintain a healthy balance between energy expenditure and calorie intake, it is highly desirable to be able to track PAE, REE, and calorie intake in an integrated system. Mault (U.S. Pat. No. 6,478,736 B1) describes a system that tracks REE with indirect calorimetry, physical activities and food consumption provided by the user, and determines energy balance from the tracked REE, physical activities and food consumption. However, tracking each physical activity, and each food item consumed by the user every meal and every day is difficult for most people.